1. Field of the Invention
The present invention relates to optometers and particularly to a Scheiner-principle optometer apparatus, and method therefor, for measuring the resting state of accommodation, and for providing cognitive recognition of this accommodative state in order to facilitate bio-feedback training of that accommodative state.
2. Description of the Prior Art
The need for precise lens accommodation to bring visual targets into sharp focus on the retina is far more urgent at night when contrast is very low, than in bright daylight. Unfortunately, it is at precisely this time that many individuals become myopic and further reduce the quality of an already poor visual image. In many professions this phenomenon, sometimes called the "dark focus of accommodation", is of little consequence. However, for pilots flying at night it can mean the difference between life and death. A reliable screening instrument capable of measuring the refractive state of individuals in the dark could, therefore, provide useful preventive information.
In the case where this preventive information is cognitively available to the subject as he accommodates, a means of implementing a bio-feedback training paradigm exists. Bio-feedback training to correct night myopia is not new. In the publication of Randle, Robert J., "Volitional Control of Visual Accommodation", Conference Proceedings No. 82 on Adaptation and Acclimatization in Aerospace Medicine, Advisory Group for Aerospace Research and Development (AGARD), North Atlantic Treaty Organization, Garmisch-Partenkirchen, Germany, September 1970, successful bio-feedback accommodation training has been demonstrated, using a Stanford Research Institute dual Purkinje image eye-tracker with optometer attachment and auditory feedback. Other apparatuses, such as the apparatus for accommodation training disclosed in U.S. Pat. No. 4,660,945, could be used in a similar fashion. However, the apparatus involved in each of these examples is large, extremely expensive and requires a trained technician to operate.